Technically... somebody could just play blitz, CTTH, alt shot, match play, etc.... to get their level as high as they want it. If they play one ranked stroke play as an amateur and score a 28, they will have a 56 average and never move up in tier unless they play more ranked stroke play rounds. Once they reach a certain amount of ranked stroke play rounds, and assuming their level is high enough, plus.. obviously his average has to be below a certain point... he will advance in tier level. I am fairly sure this info is accurate but if not, please correct me.
Good Luck,
Speedy